This invention relates to a liquid seal system particularly, though not exclusively, for a flare and/or vent stack.
Flare and vent stacks are commonly used in the petroleum, chemical and petrochemical industry to dispose of combustible gases which either constitute waste material or which have had to be released to relieve excess pressure. These stacks are frequently provided with a liquid seal through which the gases pass. This is to prevent flame flashback, to prevent air from the outlet of the stack entering the feedback to the stack, and to maintain an above atmospheric pressure in the feedline leading to the stack. An above atmospheric pressure is needed to prevent any possibility of air entering the feedline through faulty connections or the like.
There are advantages in using a liquid sealing system having an outer casing in the form of a vertical drum located at the bottom of the stack and co-axial with it. One example of the advantages of this arrangement is that it facilitates free flow of the gases: an important consideration in designing these systems.
In order to avoid entrainment of the sealing liquid into the gases, the gas velocity through the seal should not exceed 5 feet per second. The speed of the gas in the seal depends on the volume per second fed to the seal and on the surface area of the liquid. The surface area, in turn, depends on the diameter of the base drum.
Unfortunately, it is impractical to increase the diameter beyond a certain size and so, hitherto, for very large rates of gas flow, a horizontal vessel has had to be used, mounted alongside the stack. An object of this invention is to avoid this problem. Another problem of existing seals is that their sealing ability is limited. In the case of very highly inflammable gases there may be some risk of flashback jumping across the seal. Another object of the invention is to reduce this problem.